Mask assembly, deposition apparatus for flat panel displays including the same, and associated methods

ABSTRACT

A mask assembly, a deposition apparatus for flat panel displays including the same, and associated methods, the mask assembly including an open mask having a plurality of first openings, and a pattern mask coupled to the open mask, the pattern mask having a plurality of second openings disposed within an area bounded by the first openings, wherein the open mask is formed of a material having a thermal expansion coefficient that is lower than a thermal expansion coefficient of the pattern mask.

BACKGROUND

1. Field

Embodiments relate to a mask assembly, a deposition apparatus for flatpanel displays including the same, and associated methods.

2. Description of the Related Art

Flat panel displays may exhibit desirable characteristics, e.g., lightweight, low thickness, and so on. Typical examples thereof may include,e.g., liquid crystal displays (LCDs) and organic light emitting diodedisplays (OLEDs). Among them, OLEDs may be implemented as ultra thindisplays because of their excellent brightness, wide viewing angle, andabsence of a backlight, as compared to LCDs.

An OLED is a display device in which electrons injected from a cathodeand holes injected from an anode are recombined to form excitons in anorganic thin film. Radiation having a specific wavelength may then beemitted by a release of energy resulting from de-excitation of theexcitons.

In the OLED, e.g., photolithography or deposition using a mask assemblyhaving a plurality of slits formed in a predetermined pattern, may beused to selectively form a negative electrode, a positive electrode, andan organic thin film on a substrate. The substrate may be formed of,e.g., glass, stainless steel, or synthetic resin. Because moisture maybe introduced during a step of stripping photoresist using wet or dryetching during a photolithography process, deposition using the maskassembly should be used when depositing materials that may be degradedby moisture, e.g., organic thin films.

An OLED may include an organic light emitting element having red (R),green (G), and blue (B) organic light emitting layers in order todisplay a full range of colors. Deposition using the mask assembly maydeposit a thin film having a pattern corresponding to the predeterminedpattern. Deposition may occur on a substrate by aligning the maskassembly between the substrate and an evaporation source and thenallowing a deposition target to be deposited on the substrate throughthe mask assembly. Thus, to fabricate the full-color OLED, the maskassembly may include a pattern mask having the predetermined patternthereon and a frame mask supporting the pattern mask.

The mask assembly may be fabricated by an etching method including,e.g., forming slits by an etching process or an electroforming methodusing electrolysis. The etching method may be limited in its ability toform the slits in a highly precise pattern because a width of the slitand an interval therebetween may be limited by a thickness of amaterial. On the other hand, the electroforming method may be used tofabricate the slits with relatively high precision compared to theetching method.

SUMMARY

Embodiments are directed to a mask assembly, a deposition apparatus forflat panel displays including the same, and associated methods, whichrepresent advances over the related art.

It is a feature of an embodiment to provide a mask assembly havingimproved thermal stability.

It is another feature of an embodiment to provide a mask assembly beingcapable of preventing a position and shape of openings of the maskassembly from being deformed by an elevated internal temperature of aprocess chamber during a deposition process.

At least one of the above and other features and advantages may berealized by providing a mask assembly including an open mask having aplurality of first openings, and a pattern mask coupled to the openmask, the pattern mask having a plurality of second openings disposedwithin an area bounded by the first openings, wherein the open mask isformed of a material having a thermal expansion coefficient that islower than a thermal expansion coefficient of the pattern mask.

The pattern mask may be formed by an electroforming method.

The second openings of the pattern mask may form a pattern correspondingto a desired pattern of a thin film to be formed on a substrate.

The mask assembly may further include a frame mask coupled to the openmask, the frame mask having a third opening and the first openings beingdisposed within an area defined by the third opening.

The open and pattern masks may be coupled at first coupling points alongedges of the open mask and second coupling points between the firstopenings of the open mask.

The open mask may have a length and a width, the pattern mask may have acorresponding length and a corresponding width, and the length and widthof the open mask may be equal to the corresponding length and width ofthe pattern mask.

At least one of the above and other features and advantages may also berealized by providing a method of fabricating a mask assembly includingpreparing an open mask having a plurality of first openings such thateach first opening has an area, preparing a pattern mask having aplurality of second openings such that each second opening has an arearelatively smaller than the area of each of the first openings, aligningthe open mask and the pattern mask such that the second openings aredisposed within an area bounded by the first openings, and coupling theopen mask to the pattern mask, wherein the open mask is formed of amaterial having a thermal expansion coefficient that is lower than athermal expansion coefficient of the pattern mask.

Preparing the pattern mask may include performing an electroformingprocess.

Preparing the pattern mask may include forming the second openings suchthat the second openings form a pattern corresponding to a desiredpattern of a thin film to be formed on a substrate.

The open mask may have a length and a width, the pattern mask may have acorresponding length and a corresponding width, and the length and widthof the open mask may be equal to the corresponding length and width ofthe pattern mask.

Coupling the open mask to the pattern mask may include a first couplingprocess, the first coupling process including coupling edges of the openmask to edges of the pattern mask, and a second coupling process, thesecond coupling process including binding together the open mask and thepattern mask at regions between the first openings of the open mask.

The second coupling process may be carried out after the first couplingprocess is completed.

The method may further include preparing a frame mask having a thirdopening aligning the frame mask and the open mask such that all thefirst openings are disposed within an area bounded by the third opening;and coupling the frame mask to the open mask.

Coupling the frame mask to the open mask may occur after the open maskis coupled to the pattern mask.

At least one of the above and other features and advantages may also berealized by providing a deposition apparatus for flat panel displaysincluding a process chamber, an evaporation source disposed on a side ofthe process chamber, a mask assembly between the evaporation source anda substrate, the mask assembly including an open mask having a pluralityof first openings, and a pattern mask coupled to the open mask, thepattern mask having a plurality of second openings disposed within anarea bounded by the first openings, and a holder supporting thesubstrate and the mask assembly, wherein the open mask of the maskassembly is formed of a material having a thermal expansion coefficientthat is lower than a thermal expansion coefficient of the pattern mask.

The pattern mask of the mask assembly may be formed by an electroformingmethod.

The second openings of the pattern mask may form a pattern correspondingto a desired pattern of a thin film to be formed on the substrate.

The mask assembly may further include a frame mask coupled to the openmask, the frame mask having a third opening and the first openings beingdisposed within an area bounded by the third opening.

The open mask may be coupled to the pattern mask at first couplingpoints along edges of the open mask and second coupling points betweenthe first openings of the open mask.

The open mask may have a length and a width, the pattern mask may have acorresponding length and a corresponding width, and the length and widthof the open mask may be equal to the corresponding length and width ofthe pattern mask.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages will become more apparent tothose of ordinary skill in the art by describing in detail exemplaryembodiments with reference to the attached drawings, in which:

FIG. 1 schematically illustrates a deposition apparatus for flat paneldisplays according to an embodiment;

FIG. 2A illustrates an exploded perspective view of a mask assembly usedin the deposition apparatus for flat panel displays according to anembodiment; and

FIG. 2B illustrates a plan view of the mask assembly used in thedeposition apparatus for flat panel displays according to an embodiment.

DETAILED DESCRIPTION

Korean Patent Application No. 10-2009-0089699, filed on Sep. 22, 2009,in the Korean Intellectual Property Office, and entitled: “MaskAssembly, Method of Fabricating the Same, and Deposition Apparatus forFlat Panel Displays Using the Same,” is incorporated by reference hereinin its entirety.

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

In the drawing figures, the dimensions of layers and regions may beexaggerated for clarity of illustration. It will also be understood thatwhen a layer or element is referred to as being “on” another layer orsubstrate, it can be directly on the other layer or substrate, orintervening layers may also be present. In addition, it will also beunderstood that when a layer is referred to as being “between” twolayers, it can be the only layer between the two layers, or one or moreintervening layers may also be present. Like reference numerals refer tolike elements throughout.

FIG. 1 schematically illustrates a deposition apparatus for flat paneldisplays according to an embodiment. Referring to FIG. 1, the depositionapparatus 100 for flat panel displays may include a process chamber 110,an evaporation source 120 disposed on a side of the process chamber 110,a mask assembly 200 between the evaporation source 120 and a substrateS, and a holder 130 supporting the substrate S. The deposition apparatus100 for flat panel displays may further include a close contactor 300for bringing the substrate S into close contact with the mask assembly200.

A deposition process for depositing a thin film having a predeterminedpattern on the substrate S may be carried out in the process chamber110. The evaporation source 120 may store and spray a deposition targetto be deposited on the substrate S. The evaporation source 120 may bedisposed on a side of the process chamber 110. Preferably, theevaporation source 120 is disposed at a lower portion of the processchamber 110, such that the deposition target may be uniformly sprayedonto the substrate S, as illustrated in FIG. 1. The thin film depositedby the deposition process may form, e.g., an electrode, anelectroluminescent layer, etc., of a display device.

The holder 130 may support the substrate S and the mask assembly 200 toprevent the substrate S and the mask assembly 200 from being dislocatedduring the deposition process. The holder 130 may include a first holder132 supporting the substrate S and a second holder 134 supporting themask assembly 200. In an implementation, as illustrated in FIG. 1, whenthe evaporation source 120 is located at the lower portion of theprocess chamber 110, the substrate S may be located on the mask assembly200, and the mask assembly 200 may be supported by the holder 130. Thus,both the substrate S and the mask assembly 200 may be supported by theholder 130.

The mask assembly 200 may be configured such that the deposition targetsprayed from the evaporation source 120 may be deposited on thesubstrate S as a thin film having a predetermined pattern. The maskassembly 200 may include a pattern mask 220 including openingscorresponding to a desired pattern of the thin film on the substrate S.The mask assembly 200 may also include an open mask 210 coupled to thepattern mask 220.

FIG. 2A illustrates an exploded perspective view of a mask assembly usedin a deposition apparatus for flat panel displays according to anembodiment. FIG. 2B illustrates a plan view of the mask assembly used inthe deposition apparatus for flat panel displays according to anembodiment.

Referring to FIGS. 2A and 2B, the mask assembly 200 of the depositionapparatus 100 for flat panel displays may include an open mask 210having a plurality of first openings 215 and a pattern mask 220 coupledto the open mask 210. The pattern mask 220 may have a plurality ofsecond openings 225 inside the first openings 215. In other words, theplurality of second openings 225 of the pattern mask 220 may be disposedwithin an area bounded by the first openings 215. Further, each secondopening 225 may be disposed within the area bounded by only one of thefirst openings 215.

The pattern mask 220 including second openings 225 may be formed by anelectroforming method using electrolysis. Such a method may help ensurethat a highly precise pattern of second openings 225 is formed. Thus, ahighly precise pattern of thin films may be formed on the substrate S.

The open mask 210 may be coupled to the pattern mask 220. The open mask210 may, e.g., prevent a position and a shape of the second openings 225of the pattern mask 220 from being deformed by an elevated internaltemperature of the process chamber 110 during the deposition process.The open mask 210 may be formed of a material having a thermal expansioncoefficient that is relatively lower than a thermal expansioncoefficient of the pattern mask 220. Thus, the open mask 210 may inhibitthermal expansion of the pattern mask 220 during the deposition process.In an implementation, the open mask 210 may be joined or coupled to thepattern mask 220 by, e.g., adhesion, soldering, and/or welding.Preferably, the open mask 210 is welded to the pattern mask 220 inconsideration of the internal temperature of the process chamber 100during the deposition process.

Regions between the first openings 215 of the open mask 210 may serve assupports, preventing the pattern mask 220 from sagging downwards. Inorder to more firmly couple the open mask 210 to the pattern mask 220,the open and pattern masks 210 and 220 may be coupled through firstcoupling points P1 along edges of the open and pattern masks 210 and220, and second coupling points P2 between the first openings 215 of theopen mask 210. Preferably, the first coupling points P1 are firstwelding points and the second coupling points P2 are second weldingpoints.

Preferably, the open mask 210 has the same width and length, i.e. is thesame size, as the pattern mask 220. Accordingly, the open and patternmasks 210 and 220 may be easily aligned with and coupled to each other.

The mask assembly 200 may further include a frame mask 230. The framemask 230 may be coupled to the open mask 210. The frame mask 230 mayhave a third opening 235. The first openings 215 of the open mask 210may be disposed within an area bounded by the third opening 235. Such aconfiguration may allow the holder 130 to be easily coupled to the maskassembly 200.

A method of fabricating the mask assembly 200 of the depositionapparatus 100 for flat panel displays according to an embodiment will bedescribed with reference to FIGS. 2A and 2B. First, both the open mask210 having the plurality of first openings 215 and the pattern mask 220having the plurality of second openings 225 may be prepared such thatthe second openings 225 have a relatively small area compared to thefirst openings 215. In an implementation, the pattern mask 220 may beformed by an electroforming method using electrolysis such that a highlyprecise pattern may be formed. For example, the pattern mask 220 may beformed of nickel (Ni) having a thermal expansion coefficient of12.8×10⁻⁶. The open mask 210 may be formed of, e.g., a nickel-steelalloy (Invar), having a thermal expansion coefficient of 2.0×10⁻⁶, whichis relatively lower than that of the nickel.

Next, the open mask 210 may be aligned with and coupled to the patternmask 220 such that the second openings 225 of the pattern mask 220 aredisposed within an area bounded by the first openings 215 of the openmask 210. In an implementation, the joining or coupling between the openmask 210 and the pattern mask 220 may include, e.g., adhesion,soldering, or welding. Preferably, the open mask 210 is welded to thepattern mask 220, considering that the deposition process may be carriedout under high temperature in the process chamber 110.

The open mask 210 may be coupled to the pattern mask 220 by a firstcoupling process including coupling edges of the open and pattern masks210 and 220 and a second coupling process including binding or couplingtogether the open mask 210 and pattern mask 220 at regions between thefirst openings 215 of the open mask 210 such that the open mask 210 maybe more firmly coupled to the pattern mask 220. In an implementation,first coupling process may be a first welding process including weldingedges of the open and pattern masks 210 and 220 at the first weldingpoints and the second coupling process may include a second weldingprocess including welding at least certain regions between the firstopenings 215 of the open mask 210 to the pattern mask 220 at the secondwelding points. Preferably, the first welding points are formed bywelding the edges of the open and pattern masks 210 and 220 using thefirst welding process, and the second welding points are formed bywelding the regions between the first openings 215 of the open mask 210to the pattern mask 220 using the second welding process. Accordingly,the first openings 215 of the open mask 210 may not be misaligned withthe second openings 225 of the pattern mask 220 when the open mask 210is coupled to the pattern mask 220.

In an implementation, the open mask 210 may have a same width andlength, i.e. may be the same size, as the pattern mask 220. Such aconfiguration may help ensure that the aligning and coupling processesof the open and pattern masks 210 and 220 are easily carried out.

Next, the frame mask 230 supporting the open and pattern masks 210 and220 and having a third opening 235 may be prepared. The frame mask 230may be aligned with the open mask 210 such that all the first openings215 of the open mask 210 are disposed within an area bounded by thethird opening 235. Then, the frame mask 230 may be coupled to the openmask 210.

Preferably, the open mask 210 is coupled to the pattern mask 220 suchthat the open and pattern masks 210 and 220 are aligned with and coupledto each other. Then, the frame mask 230 may be coupled to the open mask210.

The deposition apparatus for flat panel displays according to anembodiment may deposit the thin film on the substrate using the maskassembly including the pattern mask 220 having the plurality of secondopenings 225. Thus, the thin film may be formed on the substrate in apattern corresponding to the second openings 225 of the pattern mask220.

The mask assembly may also include the open mask 210 coupled to thepattern mask 220, the open mask 210 being formed of the material havingthe relatively lower thermal expansion coefficient compared to thepattern mask 220. Such a configuration may prevent the position andshape of the second openings 225 of the pattern mask 220 from beingdeformed by the higher internal temperature of the process chamberduring the deposition process, even if the pattern mask 220 is formed ofa material having a relatively high thermal expansion coefficient.Furthermore, the mask assembly of an embodiment may help ensure that athin film having a highly precise pattern corresponding to the secondopenings 225 is stably deposited on the substrate.

Exemplary embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation.Accordingly, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made without departingfrom the spirit and scope of the present invention as set forth in thefollowing claims.

What is claimed is:
 1. A mask assembly, comprising: an open mask havinga plurality of first openings; and a pattern mask coupled to the openmask, the pattern mask having a plurality of second openings disposedwithin an area bounded by the first openings, wherein the open mask isformed of a material having a thermal expansion coefficient that islower than a thermal expansion coefficient of the pattern mask.
 2. Themask assembly as claimed in claim 1, wherein the pattern mask is formedby an electroforming method.
 3. The mask assembly as claimed in claim 1,wherein the second openings of the pattern mask form a patterncorresponding to a desired pattern of a thin film to be formed on asubstrate.
 4. The mask assembly as claimed in claim 1, furthercomprising a frame mask coupled to the open mask, the frame mask havinga third opening and the first openings being disposed within an areadefined by the third opening.
 5. The mask assembly as claimed in claim1, wherein the open and pattern masks are coupled at first couplingpoints along edges of the open mask and second coupling points betweenthe first openings of the open mask.
 6. The mask assembly as claimed inclaim 1, wherein the open mask has a length and a width, the patternmask has a corresponding length and a corresponding width, and thelength and width of the open mask are equal to the corresponding lengthand width of the pattern mask.
 7. A method of fabricating a maskassembly, comprising: preparing an open mask having a plurality of firstopenings such that each first opening has an area; preparing a patternmask having a plurality of second openings such that each second openinghas an area relatively smaller than the area of each of the firstopenings; aligning the open mask and the pattern mask such that thesecond openings are disposed within an area bounded by the firstopenings; and coupling the open mask to the pattern mask, wherein theopen mask is formed of a material having a thermal expansion coefficientthat is lower than a thermal expansion coefficient of the pattern mask.8. The method as claimed in claim 7, wherein preparing the pattern maskincludes performing an electroforming process.
 9. The method as claimedin claim 7, wherein preparing the pattern mask includes forming thesecond openings such that the second openings form a patterncorresponding to a desired pattern of a thin film to be formed on asubstrate.
 10. The method as claimed in claim 7, wherein the open maskhas a length and a width, the pattern mask has a corresponding lengthand a corresponding width, and the length and width of the open mask areequal to the corresponding length and width of the pattern mask.
 11. Themethod as claimed in claim 7, wherein coupling the open mask to thepattern mask includes: a first coupling process, the first couplingprocess including coupling edges of the open mask to edges of thepattern mask, and a second coupling process, the second coupling processincluding binding together the open mask and the pattern mask at regionsbetween the first openings of the open mask.
 12. The method as claimedin claim 11, wherein the second coupling process is carried out afterthe first coupling process is completed.
 13. The method as claimed inclaim 7, further comprising: preparing a frame mask having a thirdopening; aligning the frame mask and the open mask such that all thefirst openings are disposed within an area bounded by the third opening;and coupling the frame mask to the open mask.
 14. The method as claimedin claim 13, wherein coupling the frame mask to the open mask occursafter the open mask is coupled to the pattern mask.
 15. A depositionapparatus for flat panel displays, comprising: a process chamber; anevaporation source disposed on a side of the process chamber; a maskassembly between the evaporation source and a substrate, the maskassembly including: an open mask having a plurality of first openings,and a pattern mask coupled to the open mask, the pattern mask having aplurality of second openings disposed within an area bounded by thefirst openings; and a holder supporting the substrate and the maskassembly, wherein the open mask of the mask assembly is formed of amaterial having a thermal expansion coefficient that is lower than athermal expansion coefficient of the pattern mask.
 16. The depositionapparatus as claimed in claim 15, wherein the pattern mask of the maskassembly is formed by an electroforming method.
 17. The depositionapparatus as claimed in claim 15, wherein the second openings of thepattern mask form a pattern corresponding to a desired pattern of a thinfilm to be formed on the substrate.
 18. The deposition apparatus asclaimed in claim 15, wherein the mask assembly further includes a framemask coupled to the open mask, the frame mask having a third opening andthe first openings being disposed within an area bounded by the thirdopening.
 19. The deposition apparatus as claimed in claim 15, whereinthe open mask is coupled to the pattern mask at first coupling pointsalong edges of the open mask and second coupling points between thefirst openings of the open mask.
 20. The deposition apparatus as claimedin claim 15, wherein the open mask has a length and a width, the patternmask has a corresponding length and a corresponding width, and thelength and width of the open mask are equal to the corresponding lengthand width of the pattern mask.